Bombs away against cancer cells.

The war on cancer may one day have a new weapon: the gene bomb. Luis T. Da Costa and his colleagues at the Johns Hopkins University Medical Institutions in Baltimore are masterminding the novel cancer-fighting strategy. To construct the bomb inside a tumor, he explains, investigators would insert at least two foreign genes into the cancer cells.

The first gene, which Da Costa calls the trigger, encodes a protein that binds to another protein made only by cancer cells. That pairing then turns on the second transplanted gene, which codes for a bacterial toxin that can destroy the cancer cell and the cells around it. "If the cell is normal, the bomb just stays there and the cell isn't harmed. A cancer protein will pull the trigger and the bomb will go off," says Da Costa.

The gene bomb will probably end up killing some normal cells, Da Costa acknowledges. Most cancer proteins are actually mutated forms of normal proteins, so it's difficult to guarantee that the bomb's trigger will not be pulled by a normal protein. Da Costa notes, however, that surgeons usually remove healthy tissue surrounding a tumor to ensure that no cancer cells escape. In test-tube experiments, Da Costa's group has shown that this new approach can kill groups of cancer cells, including some that didn't contain the gene bomb but were near cells that did. Da Costa cautions that researchers must find more efficient ways of delivering the gene bomb into tumors.